Soaking of rayon bucket cakes before centrifugal washing



Patented July 28, 1953 SOAKING OF RAYON BUCKET CAKES BEFORE CENTRIFUGAL WASHING -Frederick Roy Millhiser, Richmond, Va., assignor to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of .Dclaware No Drawing. Application April 14, 1949, Serial No. 87,581

11 Claims. (01. 155.1)

This invention relates to the centrifugal washing and purification of bucket cakes of viscose rayon yarn.

In U. S. Patent 2,243,000 there is mentioned a method of washing and purifying bucket cakes centrifugally which briefly comprises taking an acid cake as it comes from the spinning bucket, deforming it to reduce its diameter a few per cent and then washing and purifying it in a perforated bucket of smaller diameter than the spinning bucket. By this method of washing and purifying, excess yardage is provided at the outside of the cake so that when shrinkage tendencies arise during washing and purification and later on in drying, shrinkage can take place without setting up undesirable high tensions in the yarn whether it be on the outside of the cake, on the inside of the cake or in any location therebetween. After washing and purifying, the yarn cake is centrifugally wrung in an undersized bucket which supports substantially the entire exterior of the cake at substantially higher speed than is used for washing and purifying and then is dried in the usual manner.

The above-described process is capable of producing yarn of improved uniformity from outside to inside of the bucket cake but there still remains certain undesirable features. For example, the deformation of the relatively dry cake causes damage to the yarns and filaments therein. A

freshily dofied cake of viscose rayon is quite compact and contains only about 100% coagulating bath based on the dry weight of the yarn, whereas a cake Well wet out with bath or water will contain upwards of 300% thereof based on the dry weight of the yarn. This bath is usually made up of high concentrations of salt, such as sodium sulfate, and it does not take much evaporation of water from the cake to supersaturate the solution in the cake and thus cause crystallization of the salt between the yarn layers and filaments, especially near the outer exposed surfaces. When such cakes containing only about 100% aqueous bath are mechanically deformed in any way to reduce their diameter of the order of 4%, very substantial forces must be exerted and these forces produce irreparable damage to the yarn especially when crystals exist between filaments and yarn layers.

The answer to this problem would appear obvious: simply shower the cake with water or aqueous liquid. By so doing, crystallization of the salt would be retarded, if not completely eliminated, and at the same time a lubricant would be provided between the filaments nd expected difficulties.

yarn layers so that there would be less scuffing and abrading action between yarns and filaments due to the forces deforming the cake. It is indeed surprising that this apparent, simple and direct approach to the problem involves un- The time needed to suitably soften cakes by showering with water and aqueous solutions are surprisingly long and varied as much as tenfold from one method and solution to another. Most important, undesirable luster variations result from some treatments rendering the yarn unfit for commercial use.

It is, therefore, an object of this invention to provide an improved process for centrifugally washing and purifying bucket cakes of viscose the spinning bucket withan aqueous liquid ap-' plied under such conditions that the cake is wetted through and a relatively high concentration of inorganic salt is maintained in the liquid within the cake. The concentration of inorganic saltin the liquid phase of the acid cake as doffed will normally be in the range of from 25-35% and if the wetting of the cake is done so that this concentration does not go below 5% and preferably to not less than about 8%, the luster of the finished yarn is entirely satisfactory. In general, solutions containing 15% to 30% salt are satisfactory. The salt concentration within the cake is maintained at from 5% to 30%.

The concentration is determined by reeling 3,000 yard skeins from the cake and measuring the salt content thereof. The cake outside is the most critical portionwhere the minimum allowable concentration must be maintained. The wetting of'the cakes is preferably done by dunking in an inorganic salt solution although certain soluble organic materials and other methods of application, such as controlled spraying, have proved satisfactory under certain conditions as will be apparent hereinafter. Of course, only the inorganic salts and organic materials having the requisite solubility in water may be used to advantage. The solution is used within a temperature range of from room temperature up to about 70 C. or higher. The cake treating solutions may contain in addition to any soluble inorganic salt, inorganic acids such as sulfuric acid and/or organic materials such as glucose. It may conveniently be the coagulating and/or regenerating bath in which the vis- 5 cose rayon yarn was spun. Preferred treating solutions may, for example, consist of from 20 25% sodium sulfate heated to from 30 C.-60 C. or coagulating baths containing about 20% sodium sulfate, about sulfuric acid, 1-5% zinc sulfate and 0-5% glucose preferably heated somewhat above room temperature.

After preliminary results indicated the time for suitably softening bucket cakes prior tocollapsing might be of the order of 1 hour or more, ex-- perimental means and methods were set up todetermine optimum solutions and conditions of application. A simple reproducible measuring means for determining the extent of cake softening or the ease of deformation comprised the use of two wooden blocks between which the cake was placed and collapsed flat by means of weights placed on the upper block. It was found, for example, that certain untreated cakes required a pressure of from 30-40 lbs. to collapse them fiat, whereas cakes of the same lot well impregnated with water or aqueous solution required a pressure of about 14 lbs. Certain representative data from test along this line are set forth in the table below.

Table Collapsing Weight, Pounds 13 D 1 30 npl'lpapp ica ion, Tune" application, application, 23.0% 2 3 0.06% 23.0% NazEO; Na 0 0 NaHC O3 Naif 0; plus MP- at at C. at 35 C. 189S* at MP-189$ is a sull'onatcd petroleum oil.

The values in the above table will not hold for all cake production. The absolute values vary according to cake size, yarn and filament size, bucket speed, spinning tension, etc. For any one lot of production, however, similar comparative values can be obtained although the absolute values may differ. The invention is, nevertheless, applicable to any cake of viscose rayon.

Using the figure 14 pounds as the measure of a well lubricated cake, it is seen that with a very dilute sodium bicarbonate solutionfor all practical purposes, water-and applied to the cake by dripping thereon the necessary time to reach this condition was 90 minutes, whereas with the same method of application but using a 23% sodium sulfate solution the time was reduced to one-half or minutes and with a wetting agent added to the sodium sulfate treating solution the time was further shortened to 30 minutes. However, when the cake was treated with the sodium sulfate solution by immersion therein the time of treatment was reduced to 9 minutes or only one-tenth 4 the time needed with the dilute sodium carbonate solution applied by the drip method.

While the above tests were conducted under the conditions set forth above to determine the time needed to suitably soften cakes, it has also been established. that drip washing with water or very dilute aqueous solutions greatly increases the luster of the outside layers of yarn without noticeable change to the yarn luster in the rest of the cake. This apparently is due to almost complete removal of coagulating bath ingredients from the outer yarn layers of the cake while the yarn is prevented from shrinking by the cake struct res. Analyses have shown that the outer 3,000 yards of yarn from a cake softened by dripping water or dilute sodium bicarbonate solution thereon for 30 minutes or more is reduced in concentration of bath ingredients to about 3.0-3.5 with a vely noticeable increase in yarn luster in this section. This luster change creates sufficient non-uniformity in the yarn to bar it from commercial acceptance. Yet, on the other hand, if the cake is immersed in water for from 8 to 10 minutes the yarn on the outside is not noticeably changed in luster and satisfactory cake softening results. Samples (3,000 yards) taken from the outside of the cake showed salt concentrations of from about 6.5 %7.5%. It seems that the salt solution imbibed by the yarn in the outer layers is not eliminated but remains in somewhat diluted form whereas when the cake is showered (and this method requires a relatively long time to reach the desired degree of impregnation), the outside layers of yarn are washed substantially free of salt while the rest of the cake holds solution of high salt concentration. Furthermore, when cakes are repeatedly dunked in the same vessel and the level of water or solution therein is maintained by Water buck-up, there is an accumulation of salt to the level of equilibrium concentration which is desirable.

To further illustrate this invention the following specific examples are given.

Example I A 1.1 lb. cake of -denier 40-filament bright viscose rayon yarn spun in a bucket having the following dimensions Inches Bottom diameter 6.63 Top diameter 7.06 Depth 4.60

was wrapped in a protective covering immediately after dofilng and then submerged in a 25% sodium sulfate solution at a temperature of 35 C. for 10 minutes. Thereafter the cake was collapsed according to the four-arm Topham method (see U. S, 1,736,681) to provide approximately 1 indentation for each arm. The deformed cake of reduced diameter was placed in a perforated bucket having the following specification:

Bottom diameter 6.34 inches Top diameter 7.04 inches Height Approximately 7 inches Drainage holes 120, each 0.055" in diameter arranged in five rings of 24 holes about the bucket The cake was washed and purified in the revolving bucket at a speed of 1800 R. P. M. with the following cycles:

Preliminary wash9 minutes, 0.06% sodium bicarbonate, 35 C.

Desulfuring-Q minutes, 0.35% sodium carbonate, 0.15% sodium sulfide, 0.015% sodium cyanide, 0.05% silica, 90 C.

Intermediate wash-9 minutes, soft water, 35 C.

Finish/-5 minutes with an aqueous emulsion of sulphated vegetable oil and mineral oil at 50 C.

All solutions were applied at a flow of about two gallons per minute to the inside of the cake using a suitable nozzle to insure uniform application over the whole of the cake structure. The cake was wrung in the same bucket used for washing and purification at 3900 R. P. M. for 90 seconds and then removed from the bucket and dried.

Example II A 2.7 lb. cake of 300-denier 50-filament bright viscose rayon yarn spun in a bucket having a bottom diameter of 7.35 inches, a depth of 7.50 inches and a 2 taper outwardly from the bottom to the top Was wrapped in a protective covering after doifing and then soaked by immersion for minutes in water at 30 C. The water soaked cake was deformed by means of a four-arm Topham deforming device (see U. S. 1,736,681) and then placed in a deep perforated bucket having a bottom diameter of 7.15 inches and a 1 /2 taper outwardly from the bottom to the top. The drainage holes were arranged as a single row of 8 evenly spaced holes inch up from the inside bottom of the bucket. Processing was carried out substantially as described in Example I.

In this case considerably more pressure was exerted to deform the cake than in Example I because of its larger size. Without soaking this large cake requires a pressure of 85 lbs. to collapse it. Ten minutes water soaking while maintaining a concentration of bath ingredients in the outer 3,000 yard layer of yarn at about 6.5% reduces this necessary pressure to less than 40 lbs.

Example III By constructing a liquid retaining vessel around the Topham four-arm collapsing device and simultaneously subjecting the cake to a constant deforming pressure of 40 lbs. while it is immersed in water, it was found possible to collapse the 2.7 lb. cake, of Example II, completely in about 2 /2 minutes. Thereafter, it was further processed as described in the previous examples.

The yarns so obtained in Examples I, II and III were of uniformly high quality with no noticeable dye junctions or luster variations resulting when the inside yarn from any of the treated bucket cakes was used in a fabric alongside yarn from the outside of the same cake or the outside of a different cake from the same lot processed in the same manner. A high percentage of A grade yarn cones was obtained. This signifies that no yarn degradation resulted from processing cakes in the manner above-described.

In the examples the cakes are wrapped in a protective wrapper which is permeable such as a loosely knit wrapper. While this is unnecessary, it is preferred since the yarns are protected from physical damage.

While the immersion method of impregnating the cake with softening and lubricating liquor is generally to be desired because of its faster action and more uniform distribution of salt solution throughout all parts of the cake, the cake may of course be treated in any other manner, for instance on a drip rack if concentrated solutions of salt or organic materials are used aldunking.

though the time of treatment may be lengthened to 30 or 45 minutes or longer. While a high concentration of inorganic salt or organic materials in the preliminary treating solution is necessary in a free-drain wetting process, this is not at all necessary if the wetting out step .is by However, a concentration of from about '15%-30% inorganic salt and/or organic material, such as glucose, will be found entirely satisfactory whatever the method of application. The time of treatment will vary but, in general, periods in the order of one hour are sufiicient for most purposes. Any soluble salt may be used, such as the sulfates, bisulfates, chlorides, borates, nitrates, phosphates, etc. or soluble organic materials, such as sugars, glucose, hemicellulose, etc., which are compatible with the yarn and the coagulating bath contained therein. The sodium and ammonium salts of sulfuric acid are preferred because of their availability, cheapness and good solubility. Other wetting agents than MP-189-S may be used, for example, Nacconal and lauryl pyridinium chloride.

Collapsing is necessary in order to get cakes into the undersized bucket. Any method of breaking the cake structure to reduce its overall periphery will accomplish this purpose. Topham collapsing has been used merely because it is well-known and has proved adequate. In most of the tests four-arm collapsing was used. Some tests employed eight-arm collapsing with the intent of reducing the strain at any one point, and the cakes so treated were also satisfactory, although not significantly diiferent from those collapsed with four arms. Generally, multipoint collapsing with any suitable arrangement of a plurality of arms such as 4, 8, 12, 16 or more may be used with good results.

' Any departure from the above description which conforms to the present invention is intended to be included within the scope of the claims.

I claim:

1. A process for producing high quality viscose yarn of uniform luster which comprises wetting out the bucket cake of said yarn with a softening agent, comprising a 15 to30% aqueous solution of a compound of the class consisting of the sodium and ammonium salts of sulfuric acid until said cake contains about 300% of said softening agent based on the dry weight of the yarn; thereafter multipoint collapsing said cake to reduce its overall periphery; and centrifugally bucket washing the collapsed cake while supporting substantially its entire exterior.

2. A process in accordance with claim 1 in which the wetting out is accomplished by dripping.

3. A process in accordance with claim 1 in which the wetting out is accomplished by immersion.

4. A process in accordance with claim 3 in which deformation is applied to the immersed cake.

5. A process in accordance with claim 2 wherein the wetting out extends over a period of from about 30 to about 45 minutes.

6. A process in accordance with claim 3 in which said wetting out is accomplished over a period of from about 3 to about 11 minutes.

7. A process for producing high quality viscose yarn of uniform luster which comprises wetting out the bucket cake of said yarn with a softening agent comprising a 15 to 30% aqueous solution of ammonium sulfate until the cake absorbs 7 about 300% by' weight. of said softening agent. based on the dry weight of the yarn; thereafter multipoint collapsing the cake to reduce its overall periphery; and centrifugally bucket washing the collapsed cake while supporting substantially its entire exterior.

8. A process for producing high quality viscose yarn of uniform luster which comprises wetting out the bucket cake of said yarn with a softening. agent comprising a 15 to 30% aqueous solution of sodium sulfate until the. cake absorbs about 300% by weight of said softening agent based on the dry weight of the yarn; thereafter multipoint collapsing the cake to reduce its overall periphery; and centrifugally bucket washing the collapsed cake while supporting substantially its entire exterior.

9. A process in accordance with claim 8 in which the sodium sulfate is present in a viscose rayon coagulating bath.

8, 10. A process in accordance with claim 9 wherein the wetting out is accomplished by dripping over a period of from about 30 to about 45 minutes.

11. A process in accordance with claim 9 wherein the wetting out is accomplished by immersion over a period of from about 3 minutes to about 11 minutes.

FREDERICK ROY MILLHISER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,736,681 Topham Nov. 19, 1929 2,042,529 Huttinger June 2, 1936 2,058,576 Dulken Oct. 27, 1936 2,101,361 Borzykowski Dec. 7, 1937 2,130,791 Dunham Sept. 20, 1938 2,243.000 Brown May 20, 1941 

1. A PROCESS FOR PRODUCING HIGH QUALITY VISCOSE YARN OF UNIFORM LUSTER WHICH COMPRISES WETTING OUT THE BUCKET CAKE OF SAID YARN WITH A SOFTENING AGENT, COMPRISING A 15 TO 30% A AQUEOUS SOLUTION OF A COMPOUND OF THE CLASS CONSISTING OF THE SODIUM AND AMMONIUM SALTS OF SULFURIC ACID UNTIL SAID CAKE CONTAINS ABOUT 300% OF SAID SOFTENING AGENT BASED ON THE DRY WEIGHT OF THE YARN; THEREAFTER MULTIPOINT COLLAPSING SAID CAKE TO REDUCE ITS OVERALL PERIPHERY; AND CENTRIFUGALLY BUCKET WASHING THE COLLAPSED CAKE WHILE SUPPORTING SUBSTANTIALLY ITS ENTIRE EXTERIOR. 